Route 15, consisting of the contiguous segments of State Route 15 (SR 15) joined by Interstate 15 (I-15), is a major north–south state highway in the U.S. state of California, connecting San Bernardino, Riverside, and San Diego Counties. The route consists of the southernmost of I-15, a major Interstate Highway that extends north through Nevada, Arizona, Utah, Idaho, and Montana to the Canadian border. It is a major thoroughfare for traffic between San Diego and the Inland Empire, as well as between Southern California, Las Vegas, Nevada, and points beyond.